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I found this stone on a beach in south spain, seems to have some kind of crystal formation sandwiched inside of it. Shine a light through the crack and you can see fan like formations growing inside the crystal. I have limited knowledge on gems or geology in general, any help would be much appreciated in identifying this stone/crystal.

Thank you for your reply.
The stone was found on a beach in Gibraltar, which is mostly limestone. The only mineral deposits of anything that looks like the stone are deposits of malachite in morocco. However would only explain the folded exterior rock as i cant find a malachite specimen photo online where the crystal is transparent. The rock itself has ever so slight blue hue to the green and the crystal is deep green. When a light is shone through the stone, the whole stone lights up a vivid bright green.

Gibraltar is all limestone, so that would rule out prehnite (unless it was washed up from a different location - though that is unlikely. Since there are caves in the gibraltar limestone, it is likely this is a calcite/aragonite cave formation that is waterworn and is green from organic ocean substances. If you have any strong acid see if putting it on the stone will cause it to bubble up - that would make its identity almost definitive. Also do you have any additional pictures to post?